System of ship propulsion



A g- 9 E. F. w. ALEXANDERSON 23,906

SYSTEM OF SHIP PROPULSION Filed Jan. 2, 1923 Inventor: Ernst F. W. Alexanderson,

His Attorney.

Patented Aug. 6, 1929.

UNITED STATES PATENT OFFICE.

man I. W. ALEZANDEBSON, OI, BCHENECTADY, NEW YORK, AS BIGNOB TO GENERAL ELECTRIC COMPANY, A CORPORATION 01' NEW YORK.

SYSTEM 01 SHIP PROPULSION.

My invention relates to systems of ship propulsion, and especially to an improved. system of electric s 1p pro ulsion wherein a steam turbine is used to my: ageneragor which su lies energy to a rivmg me or mechaniczilTy associated with the shlps propeller shaft. I

In the operation of ship propulsion systems which utilize a steam tur me as the prime mover, difiiculty has been encountered because of the eat difference between the speed at which t e turbine operates most efiiciently and that at which the best operatlon of the propeller is obtained. The optimum speed of a steam turbine is comparatively high. It is considered desirable in many cases to operate the turbine at a speed 1n the neighborhood of 5000 R. P. At this speed a bipolar generator supplies energy at 83 cycles per second to the driving motor which must operate at about 90 R. P. M. in order to Secure the best operation of the propeller. The operation of the driving motor at a speed of 90 R. P. M. on an 83 cycle system, however, is objectionable in that the diameter of the motor must be unduly 1nvcreased to accommodate the large number of poles required.

An object of my invention, therefore, 1s to provide an improved system of ship propulsion.

A further object is to provide a new motor aggregate particularly fitted for operation under the conditions which obtain 1n shi ropulsion.

6t er objects and advantages will appear as my invention is considered in detail.

My invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the accompan ing drawing, Fig. 1 is p a sectional view taken on the line 6-1) of 5 2 to show a part of the motor aggregate, Fi 2 is a similar view taken on line aa ofT'g. 1, and Fig. 3 is a diagrammatic view designed to show the arrangement of the system as a whole.

5 Referring now to the drawing, there is shown an adjustable speed turbine 1 arranged to rotate the field winding 2 of a generator 3, from the armature winding 4 of which electric energy may be supplied induction motor 7. The cascade connection between the induction and synchronous motors is of advantage in that it permits the use of a synchronous motor primary winding similar to the usual induction motor secondary winding. This winding comprises comparatively few turns, is adapted to be operated by large current supplied at low voltage and may readily be placed in closed slots thereby materially reducin the air-gap flux pulsations. The use of c osed slots not only, due to the elimination of air-gap pulsations, makes ossible the use of solid steel pole pieces and a uniform small aIr-gap of the same size as that of the induction motor thereby producing good magnetizing characteristics and insuring good starting torque, but also increases the effective a1r-gap area and thus reduces the amount of magnetizing current required.

As shown in Figures 1 and 2, the secondary winding 8 of the induction motor 7 and the primary winding 9 of the synchronous motor 10 are placed in suitable slots 18 and 19 formed in the laminated rotor cores 20 and 21 respectively, these cores being mounted on a member 22 connected to the hub 23 through the spokes 24. A yoke 25 is arranged to support the laminated stator core 26 rovided with slots 27 in which is placed t e primary winding 6 of the induction motor 7. Also supported by the yoke 25 are the solid steel pole pieces 28 upon which is placed the exciting winding 16. The use of solid steel pole pieces is of particular advantage, in that the slip energy during induction motor operation is largely developed in the body of the pole pieces from whence it is readily dissipated, and in that the skin effect is utilized to give high resistance characteristics at starting when the frequency of the current induced in these pole pieces is comparatively high.

If. it is desired to modify the skin efiect characteristics of the solid steel pole pieces so as to give a higher synchronous torque, a squirrel cage winding 17 may be placed near the faces of the pole pieces, the desired combination of short circuiting effect by the squirrel cage winding and s in effect in the pole pieces being regulated by the number of bars in the squirrel cage winding.

A suitable source of direct current 13 may be provided for supplying the necessary excitation to the field winding 2 of the generator 3 and the field winding 16 of the synchronous motor 10 through switches 14 and 15 respectively.

Longitudinal holes 29 through the ole pieces 28 are provided near the pole aces for the purpose of controlling the air-gap flux distribution and supporting the squir- .e1 cage Winding 17. These holes are spaced so that the iron between them is restricted to give the desired degree of magnetic saturation, the holes near the corners of the pole pieces being drilled more closely than at the middle with a view of producing approximately a sine wave distribution of flux.

Advantage is thus taken of the peculiar requirements of ship propulsion by departing from the usual design of synchronous motors in such a Way as to particularly fit this synchronous-induction motor aggregate for use in the propulsion of ships.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. A concatenated induction-synchronous motor aggregate, the synchronous motor having solid metal pole pieces and a core member provided with closed slots, the primary winding of said synchronous motorbeing placed in said slots.

2. In combination, an induction motor and a synchronous motor, the secondary n'aaeoe winding of said induction motor liein connected to the primary winding of sai synchronous motor whereby said induction and synchronous motors form a concatenated aggregate, said synchronous motor having solid metal flpole pieces to produce at starting a high e ective resistance in the secondary of said induction motor.

3. A concatenated induction-synchronous motor aggregate, the synchronous motor having a core member provided with closed slots in which the primary winding is placed, said synchronous motor being provided with solid pole pieces in the faces of which are provided a series of longitudinal holes arranged to produce an approximate sine wave distribution of flux over the pole faces.

4. A synchronous-induction motor aggregate comprising a rotor core provided with closed slots, an induction motor having its secondary winding arranged to rotate with said rotor core, and a synchronous motor having its primary winding wound in, said slots, the stator of said synchronous motor being provided with solid metal pole pieces perforated to produce an approximate sine wave distribution of air gap flux.

5. A synchronous-induction motor aggregate comprising a rotor core providedwith closed slots, an induction motor having its secondary winding arranged to revolve with said rotor core, a synchronous motor having its primary winding wound in said slots and having stationary ole pieces of solid metal perforated to pro uce an approximate sine wave distribution of air gap flux, and a high resistance squirrel cage winding in certain of said perforations.

In witness whereof, I have hereunto set.

my hand this 29th day of December, 1922.

V ERNST F. W. ALEXANDERSON. 

